The proposed research is aimed at bridging the gap of knowledge between the biochemistry, ultrastructure and cell physiology of cytoplasmic structure and contractility in non-muscle cells. The experiments take advantage of the developments from the last grant period in identifying actin-binding proteins, in developing quantitative fluoresence micropscopic assays, in proposing a working hypothesis on the relationship between cytoplasmic structure and contraction, and in implementing quantitative imaging techniques for basic questions in cell biology. The proposed experiment will continue the plan of integrating information obtained from motile cell extracts, reconstituted cell models, and from living cells. Changes in free [Ca++], pH, solation of the actin-based cytoskeleton, and contraction will be measured in in vitro models and in living cells. In addition, a critical test of the solation-contraction coupling hypothesis is proposed.